Implement HTTP request in offchain workers (#3461)

* Implement HTTP request in offchain workers

* Bump impl_version

* Don't compile offchain workers for WASM anymore

* Initialize HttpConnector as a fallback.

* Apply review suggestions 😳

substrate/core/sr-io/src/offchain/http.rs

@@ -224,7 +224,7 @@ pub enum Error {
 	/// Deadline has been reached.
 	DeadlineReached,
 	/// Request had timed out.
-	Timeout,
+	IoError,
 	/// Unknown error has been ecountered.
 	Unknown,
 }
@@ -283,8 +283,8 @@ impl PendingRequest {
 			.zip(requests.into_iter())
 			.map(|(status, req)| match status {
 				RequestStatus::DeadlineReached => Err(req),
-				RequestStatus::Timeout => Ok(Err(Error::Timeout)),
-				RequestStatus::Unknown => Ok(Err(Error::Unknown)),
+				RequestStatus::IoError => Ok(Err(Error::IoError)),
+				RequestStatus::Invalid => Ok(Err(Error::Unknown)),
 				RequestStatus::Finished(code) => Ok(Ok(Response::new(req.id, code))),
 			})
 			.collect()